Version 7 is available for preview. It includes a number of improvements with respect to provisioning (although these improvements are largely as a provisioner, rather than a provisionee!).

Provisionee (via HostBill template)
With respect to your question of Provisioning MailEnable itself, we are currently testing provisioning templates via the WebServices interface released earlier this year (specifically the creation of an APS package to allow provisioning via APS control panels - ie: Plesk).

When this is complete will will investigate how MailEnable may be able to be provisioned by HostBill. MailEnable has libraries for provisioning via PHP over web services.
HostBill seems to simply require a PHP script that will call into that library - so it should not be too difficult to integrate.

Provisioner (automating other services)

1. When new postoffices/domains are created (or removed), you can shell an application/script (ie: you can use this to provision any additional services).

2. It provides templates for provisioning its own services. Eg: you can configure default options for new postoffices/domains and users.
For example, when webmail is configured for a postoffice, DNS and IIS are automatically updated with the required changes.

3. It is also possible to develop provisioning plug-ins that appear directly within the MailEnable interface as optional components.

Example: there is currently one that provisions a web site on postoffice creation and a simple example that simply logs to a text file with an audit of system changes.
We have also discussed whether we should develop a plug-in that deploys a basic web site, along with the ability to edit the content online.
We intend to provide a template visual studio project that assists in integrating provisioning with other applications.

Whilst MailEnable Version 7 has the capability to automate and provision additional services, there are products (like Plesk or WebSitePanel) that specialise and are designed as provisioning engines.
If you simply want to set up a new organisation with e-mail, webmail, dns and a web site - then MailEnable version 7 will allow you to do that.
If you want something more exotic - like provisioning wordpress or specialist applications, then a dedicated Control Panel Solution will most likely provide it out of the box.

I'm glad to hear templates are coming in V7 with possible hostbill integration later. I think I'll look into what it would take to write our own interface for hostbill.

I'm not sure a plugin to edit web sites is something that Mailenable should get into. It sounds like a distraction.

What I would really love to see is a plugin for Plesk or cpanel that would allow these control panels to setup and manage email on seprate, standalone email server. I'd pay a reasonable price for that with annual maintenance.

I have Plesk Linux and Windows hosting servers and I've never liked maintaining separate mail servers and I don't like the email server options in the Linux realm. I decided to run a separate, standalone email server anyways and have moved most of my users from Linux and Windows plesk onto this server. They have to manage Plesk and Email separately which isn't ideal but I think I provide a better email solution doing it this way.

My long term goal is to reintegrate that back into the Control panel when I have the resources to do so.

I think you'd sell a lot more plugins that provide this functionality than a plugin that edits web sites and really, do you want to compete with Wordpress?

So are you saying that Mailenable will be coming out with a plugin that will allow me to provision email accounts for individual domains but on a central email server from any Plesk web server?

I would pay for that with annual maintenance.

Something else to consider is CRM add ons for Mailenable. It seems to me this is all converging and we risk losing clients to SugarCRM, Salesforce and the many other which essentially provide email but with all the extras.

I wouldn't try and compete with Sugar or Salesforce feature for feature but target simpler, easy to manage solutions for small and medium size business that doesn't want to pay a fortune or per user. Something like what teamlab offers.